The present invention relates to a novel polyimide and more particularly to the polyimide which is almost colorless, capable of being extrusion or injection molded and is furthermore excellent as high-temperature adhesive.
Conventional polyimide obtained by the reaction of tetracarboxylic dianhydride with diamine has excellent electrical and mechanical properties in addition to its good high-temperature stability. Therefore the polyimide has been used in many fields such as electric and electronic members, space and aeronautic materials and automotive parts and is currently expected for the application to further various fields.
However, the polyimide which has so far been developed is generally low in light transmittance and mostly yellow or brown colored, although many of the polyimide exhibit excellent properties. For example, polyetherimide having the formula (II) "Modern Plastics International, June 1982, pages 38 to 39" has been known as polyimide having a high total light transmittance. ##STR3##
The film of the polyetherimide is almost colorless and is 35% in transmittance of light beam having a wave length of 400 nm at a thickness of 50 micrometers.
However, for use in the covering pad of solar cells in the recent space development program, polyimide is required to have a further high transmittance for total light, particularly a high transmittance in the wave length region of 400 nm which is the subject of space, and additionally have an excellent processability.
Besides the conventional polyimide has poor processability. On the other hand polyimide having good processability is inferior in the high-temperature stability and solvent resistance. Thus the performance of polyimide has both merits and drawbacks.
For example, the polyimide having recurring units of the formula (III): ##STR4## has been known to have high-temperature stability (for example, Kogyo Zairyo, 27, 98 (1979)). This polyimide, however, has no distinct glass transition temperature and is required to mold by special means such as sintering.